The invention relates to a color picture display device comprising a color picture display tube having at least a final anode and a screen grid electrode, a high tension generator for generating a high tension for the final anode and a line deflection generator for generating a line deflection current through a line deflection coil and comprising a rectifier for rectifying line flyback pulses for generating a supply voltage for the screen grid electrode, said generators being separated from one another, furthermore comprising a field deflection generator for generating a field deflection current through a field deflection coil and an east-west raster correction generator for the field frequency parabolic modulation of the amplitude of the line deflection current.
Such a color picture display device is known from the publication "Philips Application Information No. 238: Color television receiver with separated e.h.t. generator" dated Feb. 18, 1966. With a device wherein high tension is not derived from the line deflection generator, there is the possibility that the high tension is present while the line deflection generator is defective. The electron beam(s) generated in the picture display tube is (are) then present but there is no horizontal deflection, which may cause burning-in of the picture of the tube. Said publication explains advantages of a separated e.h.t. generator. A more recent reason for using separated generators is the fact that the high tension can be generated by a switched-mode power supply which can also generate other supply voltages for other sections of the display device and which has been increasingly used of late in view of its specific advantages.
To prevent the above-mentioned damage to the picture tube, the screen grid voltage is obtained in said publication by rectifying line flyback pulses of the line deflection generator. If this generator stops, the electrons in the picture tube are not accelerated sufficiently, and therefore, the beam current is cutoff. However, with color picture display devices, the line deflection current is subjected to an amplitude demodulation for the east-west raster correction. The screen grid voltage must not follow this modulation, which would cause an annoying brightness modulation, but, in view of the above-mentioned protection, this voltage must be smoothed with a time constant which is not too large, so that the rather low-frequency east-west component (50 or 60 Hz) is substantially not removed. In the prior art devices, this was not experienced as a drawback because the picture display tube thereof had a comparatively small deflection angle, namely 90.degree., for which tube the depth of modulation of the line deflection current need not be so large as for tubes having a larger deflection angle.